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Atopy diagnosis time consuming for DVMs and owners

Atopy or inhalant allergy in the cat is probably underdiagnosed because of cats' ability to respond so well to steroids.

Photo 1: This cat is suffering from inhalant allergy with preauricular erythema and allergic otitis.

However, as we all know with repeated steroid use in the cat, diabetes mellitus is a dangerous consequence. Recent reports of steroid-induced cardiomyopathy are also of serious concern. With the most common inhalant allergen in the cat being dust mites — a year round problem — it is not advisable to maintain the patient on continuous steroid therapy particularly when other therapies for allergy are available.

We have all recognized atopic cats in our practices, but, scientifically, atopy has yet to be proven in cats. To date, feline IgE has not been isolated and identified. However the presence of a reaginic antibody has been demonstrated via passive cutaneous anaphylaxis (PCA) in healthy cats injected with serum from atopic cats. The molecular weight of this feline reaginic antibody is similar to IgE in other species and feline "IgE" cross reacts with canine IgE, all alluding to the existence of feline IgE.

Looking for signs
Clinical signs and symptoms of atopy in cats can vary greatly compared to atopic symptoms in dogs. Some effected cats show parallel symptoms of atopy in dogs with face rubbing, rectal itching and foot licking/biting. Others present with symmetrical alopecia of the trunk and hocks, and just general excessive grooming. Recurrent otitis, eosinophilic granuloma complex lesions including rodent ulcers and "pouty chins," miliary dermatitis and chin acne can all be symptoms of feline atopy. In our practice, most cats effected are young or middle-aged, and the majority have "orange" in their color (either calicos or orange tabby's). Age of onset can be difficult since many cats are adopted at an unknown age or live outside for awhile then are brought inside and become allergic.

Photo 2: Note the chin acne in this atopic cat. Atopy is an important differential in feline acne.

Unless there has been a significant change in the patient's environment, we usually do not see atopy in elderly cats. Probably the most common purebred cat we see with atopy is the Devon Rex, and symptoms usually present at a young age.

Perhaps the most difficult aspect of treating atopy in the cat is, in fact, determining that the cat is atopic.

Many of the differentials of atopy in the cat are steroid responsive which is the reason steroids tend to be used so much in this species.

However as scientists, we have the ability to use laboratory diagnostics, including skin scrapings, cultures or blood tests, to rule in or rule out differential diagnoses.

When to inject?
It certainly requires less time to administer a steroid injection to a pruritic cat, but are we truly doing that patient justice? Before arriving at the diagnosis of atopy, which truly is a disease of exclusion, we need to rule out several other differentials including ectoparasites (fleas, Cheyletiella mites, demodex gatoi, Notoedres), dermatophytosis, food allergy, pemphigus foliaceus, bacterial pyoderma (somewhat rare in the cat) and Malassezia dermatitis.

Ruling out ectoparasites can be difficult, especially in a multi-cat household or in a household that fosters pets. Flea allergy in the cat does not present with a typical dorsal lumbar alopecia as in the dog, but it does a mixed bag of symptoms such as those mentioned previously. All the pets in the household need to be checked for fleas and treated with an adulticide product, and the household should be treated with an environmental spray.